1. Field of the Invention
This invention relates to the welding art and more particularly to melting fluxes for submerged arc welding which have improved detachability of slag and are free of slag inclusion when applied to high speed welding.
2. Description of the Prior Art
In the manufacture of various types of equipment and tanks for chemical industries using thick steels, it is the general practice that a large proportion of time in the manufacturing process is occupied by welding time. Accordingly, welding materials used for such purposes should ensure good welding workability and should not produce welding defects which require later correction. One of the factors which influences welding workability is the above-mentioned detachability of slag from the weld metal. When submerged arc welding is conducted using a flux which is poor in slag detachability, much labor and time is required to remove once-formed slag. If the slag is insufficiently removed, welding defects such as failure in welding penetration, slag inclusion, and the like take place when a subsequent layer is welded. To avoid this, many studies have been made to improve slag detachability, the present invention being such an improvement.
In order to improve slag detachability, there have been heretofore proposed fluxes which incorporate Al.sub.2 O.sub.3, TiO.sub.2, SiO.sub.2, and the like in suitable amounts, such as are disclosed in Japanese laid-open Patent Publication Nos. 55-10356, 55-10357, and 55-10358.
However, when low heat input and high velocity welding is conducted using fluxes which contain more than 20% Al.sub.2 O.sub.3, there may occur a slag inclusion phenomenon in which slag is included in the molten metal where it solidifies in the weld.
In order to reduce the amount of Al.sub.2 O.sub.3 in fluxes and to improve the detachability of slag, we have made an investigation of factors which influence detachability. Though a number of the factors that influence detachability have been known, including solidifying temperature, viscosity, wettability, thermal expansion coefficient, and the like, it has been found most important that slag should not spread out in the root gap, especially in the case of narrow grooves. To achieve this favorable end, it has been found that a flux should have a relatively high solidifying temperature and a high viscosity at high temperatures. Thus, we have made extensive studies of fluxes which satisfy the above requirement, in which various kinds and proportions of flux constituents are compared.